It has been required for a semiconductor integrated circuit to have a higher speed operation and a higher density integration as, in recent years, an electronic equipment applied to the semiconductor integrated circuit has been improved in performance. In order to fulfill such a request, it is necessary to solve a problem relating to noises generated in an integrated circuit.
It has been known to reduce internal noises, hitherto, there is known a procedure to employing a layout of an integrated circuit in which the internal noises are hardly generated because a distance between, signal lines is increased to prevent a crosstalk. It is also known to connect a relatively large capacity load to a signal line so as to prevent an overshoot or undershoot from being generated in the circuit.
Under present conditions, the procedure of obtaining a semiconductor integrated circuit in which the noise is hardly generated depends on a trial and error design of increasing the distance between the signal lines and of realizing a higher density integration. Even if a simulator of high accuracy is used, an optimal design of an integrated circuit is very difficult. Moreover, even if an optimally designed layout is prepared, there is a limit in reduction of the noises which are generated during the high speed operation of a high density integrated circuit.
The method of connecting the capacity load to the signal line to prevent the generation of the noise is not suitable for the high density integration since the capacitor is large in size.
JP-A-57-188122 (the term "JP-A" used herein means that the patent application was laid open to public inspection but has not been examined) by Inoue discloses a filter for eliminating high frequency noises by connecting a capacity load to a signal line to reduce internal noises. The filter of Inoue is formed in a package enclosing by-pass capacitors to be inserted between each terminal of a package of a dual-in-line type integrated circuit and the ground. The package has the same number of pins as that of the integrated circuit package. Moreover, the filter of Inoue is mounted in such a way as to be hierarchically superposed on the integrated circuit chip. The filter disclosed by Inoue is considerably small and is capable of being used integrally with the integrated circuit for reducing noises in the integrated circuit. Since the filter of Inoue has a size substantially equal to that of the integrated circuit, although it can be superposably mounted, it cannot sufficiently comply with the request for the higher density integration.
Moreover, in the case where for the purpose of further improving the integration, capacity elements are integrated in the semiconductor integrated circuit, a considerable area must be secured on the chip. Therefore, it is difficult to form a high density integrated circuit.
Incidentally, since the capacity elements cause a response speed to be lowered, this is contrary to the request for attainment of the higher speed operation.